The ISDN (Integrated Services Digital Network), which allows, in addition to speech transmission, the rapid transmission of data, texts, and pictures also enables NT and TE apparatus as well as other distribution nets to be connected at its interfaces. Irrespective of a net-side interconnection of ISDN terminal equipment (TE) or network terminations (NT), the enlargement of the range of the transmission channel between functional groups of the ISDN-user interface with reference to an ISDN interface is of advantage for the transmission of the information of the net over a longer distance. However, the range achievable with traditional means is significantly limited due to the electrical features of the ISDN interfaces and connection ways.
From DE 44 07 214 C1, a technical solution is known which in spite of the restrictions of the physical state existing at the interface of an ISDN-user interface, allows to enlarge the range of the transmission channel between functional groups of the ISDN-user interface. In this solution, the ISDN-specific coded data incoming or, respectively, being required at the ISDN interfaces are converted into binary-coded data on the net (or network; as used herein, net refers to network) side as well as on the terminal side. The binary-coded data are grouped into blocks and directed to a transmission means to be corresponded on the net- or terminal-side, respectively. Due to the standardized structure of, for example, an ISDN basic terminal with 2.times.64 kbit/s of the B-channels or 1.times.16 kbit/s of the D-channel and the necessary signaling and control information the transmission means transmits, according to DE 44 07 214 C1, information with a bandwidth of 160 kbit/s, which is a considerable and expensive bandwidth of the data transmission via, for example, a satellite channel. Data transmission, particularly via satellite channels, considerably demands reduced bandwidths or, respectively, exactly defined bandwidths of, for example, 64 or 128 kbit/s. A number of satellite services run terminals with 64 kbit/s channels.
Therefore, it is the object of the invention to create a method and apparatus which allow the range of the transmission channel between functional groups of the ISDN-user interface in relation to an ISDN interface to be extended under the condition of a minimized bandwidth. This is achieved maintaining all ISDN-specific features, such as
maintenance of the network timing PA1 multiple access to the interface bus PA1 activation and deactivation of the interface.